Method of stabilizing trichloroethylene



United States Patent 3,417,152 METHOD OF STABILIZING TRICHLOROETHYLENEGermano Patron, Milan, Italy, Ottavio Merluzzi, Toronto,

Ontario, Canada, and Antonio Ferri, Milan, Italy, assignors toMontecatini Edison S.p.A., Milan, Italy No Drawing. Continuation ofapplication Ser. No. 420,852, Dec. 4, 1964. This application May 31,1966, Ser. No. 554,220 Claims priority, application Italy, Mar. 11, 19601,675/ 60 1 Claim. (Cl. 260-6525) This application is a continuation ofSN. 420,852, now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 76,466, filed October 19, 1960 (now abandoned).

The present invention relates to the stabilization of chlorinatedhydrocarbons and, more particularly, to a method of stabilizingtrichloroethylene, as well as the composition produced by this method.

As pointed out in our above-identified copending application and as willbe apparent from the commonly assigned U.S. Patent No. 3,000,977, issuedSept. 19, 1961, to two of the present joint inventors, trichloroethylenecan be stabilized by the admixture therewith of nitrogen-containingadjuvants of a weakly basic character. This stabilization of chlorinatedhydrocarbons and especially trichloroethylene is essential in practice,since the latter compound is a solvent widely used for the decreasing ofmetals, the drycleaning of fabrics, and solvent extractions. In additionto being highly volatile and thus able to be recirculated after use anddistillation, it is liquid at ambient temperature and has excellentsolvent capabilities. It has, however, one significant disadvantage,namely its propensity toward self-catalyzed decomposition to produceacids upon oxidation of the chlorinated hydrocarbons. Thus,trichloroethylene, in the absence of any stabilizers or the like, will,upon exposure to air, produce hydrochloric acid whose presence catalyzesfurther decomposition of the solvent. it has been proposed heretofore tostabilize the solvent against such decomposition by adding theretocompounds having a weakly basic character and thus being adapted toneutralize the acidity which otherwise would tend to catalyze thedecomposition, or preferentially oxidizable materials which, as aconsequence of their selective oxidation by atmospheric oxygen, preventan equivalent degree of decomposition of the trichloroethylene. Thus, ithas been proposed to form compositions of the chlorinatedfhydrocarbonswith amines and epoxides which neutralize acid as formed and phenolswhich are preferentially oxidized to quinonic forms. The decompositionof trichloroethylene yields not only hydrogen chloride but alsophosgene, a highly toxic and nausea-inducing compound.

It is the principal object of the present invention to provide animproved method of stabilizing chlorinated hydrocarbons and, especially,trichloroethylene.

It is a further object of this invention to provide a stabilizedtrichloroethylene composition in extension of some of the principles setforth in our above-mentioned copending application and free fromdisadvantageous results characterizing earlier stabilization systems, asnoted hereinafter.

In any system for the stabilization of chlorinated hydrocarbons, andespecially trichloroethylene, it is important that the followingcriteria must be observed:

(a) The stabilizing agent or agents must be at most only weakly basic topreclude attack upon amphoteric metals (e.g., aluminum, zinc and alloysthereof) with which the trichloroethylene is commonly used for theremoval of greases. In the case of these metals, both the acidityresulting from decomposition and the basicity Patented Dec. 17, 1968 iceresulting from any use of highly basic stabilizers, are equallydisadvantageous.

(b) The degreasing of metal is carried out generally in the vapor phaseand the stabilizers and decomposition inhibitors must be present in thevapor phase as well as in the liquid phase. This is all the moreimportant when it is realized that vaporization of trichloroethylenerenders it highly susceptible to decomposition by atmospheric oxygen.

(c) The stabilization compounds must be such as not to impede materiallythe operation of the solvent, either by virtue of the quantity of thedecomposition inhibitor present or by the nature of its structure.

Thus, the present invention is directed to the stabilization ofchlorinated hydrocarbons, especially trichloroethylene, in a mannerwhich will inhibit the formation of phosgene and thereby obviate anydifiiculties arising from the presence of this noxious substance indegreasing plants and the like, while precluding the formation ofhydrogen chloride by hydrolysis of the phosgene; the hydrochloric acidis, as is well known, extremely corrosive to the equipment and degreasedmetallic parts. The stabilizing compositions should, according to thepresent invention, include a reliable anti-oxidant, should be free fromsubstances of highly basic character, and should have a boiling pointclose to that of trichloroethylene. The basicity of theantidecomposition substances are, for the present purposes, evaluatedfrom the pH of the water extract of the solvent composition. Thus, thispH should be about 7.

We have now found that all of these characteristics are fulfilled bydecomposition-inhibiting agents including formaldehyde dialkylhydrozonesof the general formula:

wherein R is an alkyl group, preferably methyl. Thus, stabilizedcompositions of the present invention should include dimethyl hydrazoneswhich is variously known also as methylene dimethylhydrazone andmethanal dimethyl hydrazone. In our copending application Ser. No.76,466, filed Dec. 19, 1960, now abandoned, we have disclosed thataldehyde dialkylhydrazones constitute a marked improvement overhydrazine derivatives of the general formula:

when employed for the stabilization of trichloroethylene. It was alsonoted in this application that, in general, equivalent quantities byweight of the methylene (formaldehyde) dialkylhydrazone and thecorresponding ethylidene (acetaldehyde) dialkylhydrazone gave poorerresults with the latter compound than with the former. It has now beenfound that the superior character of the formaldehyde dialkylhydrazonepermits considerably less of it to be employed for the stabilization oftrichloroethylene with consequent advantages. Thus, it has been notedthat acetaldehyde dialkylhydrazone, for example, is less significant inthe vapor phase for the most part and, in any event, is certainly lessavailable than is formaldehyde dimethylhydrazone. Moreover, surprisinglyless of the formaldehyde dimethylhydrazone is required than theacetaldehyde dimethylhydrazone. Discoloration of the liquid and vaporphases is reduced while difliculties encountered in the use of thehigher-molecular-weight compound (i.e., acetaldehyde dialkylhydrazone)with respect to loss, decomposition and discoloration uponrepurification of the solvent are avoided.

More specifically, it has been found that, broad disclosures in the artnotwithstanding, a reduction in the proportion of acetaldehydedimethylhydrazone in the tri-chloroethylene composition of 0.01% byweight, i.e., 100 parts per million (p.p.m.), results in a sharp dro inthe stabilizing capacity of the acetaldehyde dimethylhydrazone. Incontradistinction, the formaldehyde-dimethylhydrazone system of thepresent invention can have as low as 0.001% of the hydrazone (by weight)and preferably contains between 0.001% (10 p.p.m.) and 0.008% (80p.p.m.) of formaldehyde dimethylhydrazone although amounts up to 0.01%are effective and 0.02% (200 p.p.m.) does not involve a significantreduction in effectiveness but other disadvantages begin to arise. Thus,it is an essential feature of the present invention that the improvedstabilizing composition contains less than 0.01% by weight (100 p.p.m.)of formaldehyde dimethylhydrazone but an excess of about 0.001% (10p.p.m.), based upon the weight of trichloroethylene.

As described in our copending application referred to above, theformaldehyde dimethylhydrazone should be incorporated in the solventtogether with at least one epoxide component, in an amount rangingbetween 0.01% (100 p.p.m.) and 1% (10,000 p.p.m.) by weight of thesolvent, and preferably from 0.05% (500 p.p.m.) to 0.3% (3,000 p.p.m.)by weight; the other constituent of the mixture can be a phenol presentin an amount between 0.001% (10 p.p.m.) and 0.05% (500 p.p.m.) byweight, preferably from 0.001% (10 p.p.m.) to 0.01% (100 p.p.m.).Diisobutylene can be substituted for phenol. Suitable phenols includethymol, p-tertiaryamyl phenol which may be present in amounts between0.001 to 0.01% and hydroquinone monomethyl ether which may be present inamounts 0.001 and 0.1% by weight trichloroethylene.

The following specific examples illustrate the principles of the presentinvention.

Example I Substituted hydrazines such as the dialkylidene-N,N'-hydrazones are compared with alkylidene dialkylhydra- Zones and thelatter compounds are compared among themselves as follows:

In accordance with the procedures set forth in Army- Navy AeronauticalSpecification U.S. MIL-T 7003 of Sept. 5, 1950, trichloroethylene wasstabilized by the addition of the various compounds and subjected to theaccelerated oxidation test of this standard. In accordance with thisstandard, 200 ml. of the stabilized composition are subjected to 48hours of reflux boiling into a stream of water-saturated oxygen using a150watt sandblasted lamp as the heat source. Steel plates are disposedin the liquid and vapor phases to determine the corrosivity and thecomposition is extracted with water to test the pH. The phosgene contentis determined from the composition by conventional means. The resultsare as follows:

(A) When compositions of trichloroethylene are stabilized with 0.02% ofdiethylidene-N,N hydrazone (CH CH:N-N CHCH and diisopropylidene-N,N'hydrazonc [(CH C=NN C(CH the water extract had a pH of 2 and thecomposition was found to be saturated with phosgene. 0.04% by weight ofeach of these compounds yielded identical results.

(B) Ethylidene dimethylhydrazone or acetaldehyde dimethylhydrazone in anamount of 0.02% by Weight yielded a water extract Whose pH was between 4and 5 and produced a composition showing traces of phosgene. 0.04% ofthe amount of this latter compound in the composition raised the pH tobetween 5 and 6. When the proportion was 0.025% by weight, thecomposition yielded a pH of about 6 for the water extract, while areduction in the proportion to 0.01% results in a pH of 3 to 4. In thelatter case the vapor phase was found to be corrosive and thecomposition had a brown coloration. Any attempt to further lower theproportion of the acetaldehyde dimethylhydrazone resulted in a sharpincrease in the production of acid as observed from the water extract.Tests made with the acetaldehyde diethylhydrazone gave similar results.Traces of phosgene were, however, found in the case of the acetaldehydedimethylhydrazone.

(C) The test was carried out with 0.25% by weight methylenedimethylhydrazone, i.e., formaldehyde dimethylhydrazone and the pH ofthe water extract (the solvent composition being always extracted withan equal volume of water) was found to be 7.00 after the acceleratedoxidation test. When 0.02% by weight of this hydrazone was employed, thepH was again found to be about 7 for the water extract and no phosgenewhatsoever was observed. Reduction of the proportion of the formaldehydedimethylhydrazone to 0.01% reduced to a slight extent the pH of thewater extract upon accelerated oxidation, although stabilization wasstill effected and the vapor phase found to be noncorrosive even whenthe proportion was reduced to 0.005% (5 p.p.m.) When this proportion ofacetaldehyde dimethyl hydrazone was employed, no stabilization wasobserved.

Example lI.Composition including an epoxide (A) The acceleratedoxidation tests described above were carried out with 0.25% by weight ofacetaldehyde dimethylhydrazone and 0.20% butylene oxide. The relativelyclear composition was found to have a H slightly less than 6.9 and thevapor phase was found to be noncorrosive and clear. When, however, theproportion of racetaldehyde was reduced to 0.01 weight percent, the pHdropped to between 5 and 6 for the water extract and poor stabilizationresulted. At a proportion of formaldehyde dimethylhydrazone of 0.01%,the pH Was found to be just below 7 with the same proportion of theepoxide component. When the formaldehyde-dimethylhydrazone proportionwas further reduced to 0.005% by weight, effective stabilization wasstill obtained, whereas the composition containing acetaldehydedimethylhydrazone at this proportion was totally unsuitable.

(B) When 0.20% by weight of propylene oxide was substituted for thebutylene oxide of Example II(A) above, 0.01% acetaldehydedimethylhydrazone gave a pH between 4 and 5 for the water extract, abrown coloration, accelerated oxidation and a discolored vapor phase. Bycontrast, the formaldehyde dimethylhydrazone of the present inventionhad a pH not less than 6 and a noncorrosive vapor phase. Reduction ofthe proportion of the lat ter compound in the composition to 0.005% byweight still yielded satisfactory stabilization.

(C) When equal parts by weight of propylene oxide and butylene oxidewere used in these compositions, results generally similar to thoseobtained with only butylene oxide as the epoxide were discerned.

Example III.Hydrazone, epoxide and phenol composition (A) Atrichloroethylene composition containing 0.01% by weight of formaldehydedimethylhydrazone for the hydrazone of part A above gave a pH of 7 andwas characterized by a clear (undiscolored) liquid phase and a similartranslucent vapor phase. Reduction of the formaldehyde dimethylhydrazoneconcentration to 0.005% by weight of the trichloroethylene gaveeffective stabilization whereas a similar reduction in the concentrationof acetaldehyde dimethylhydrazone rendered the composition unsuitablebecause of its high acidity and tendency to decompose.

(B) The proportions of Example III(A) were employed except that thephenol was p-tertiaryamyl phenol with a concentration of acetaldehydedimethylhydrazone of 0.01% by weight; a pH of less than 7 was observedby contrast to the pH of 7 obtained with an identical quantity offormaldehyde dimethylhydrazone. Again, further reduction in theconcentration of the hydrazone resulted in complete loss ofstabilization qualities for the acetaldehyde dimethylhydrazonecomposition, while stabilization was maintained to a concentration ofabout 0.001% by weight with the formaldehyde dimethylhydrazone.

Example 1V.Hydrazone, epoxide and quinone composition (A)Trichlorethylene was stabilized with a system consisting of 0.01% byweight of acetaldehyde dimethylhydrazone, 0.1% butylene oxide, 0.1%propylene oxide and 0.005 hydroquinone monomethyl ether. The pH of thecomposition was found to be about 6 and further lowering of thehydrazone concentration reduced the pH further and eliminated anystabilization qualities of the composition. When a similar compositionwas prepared with 0.01% by weight of formaldehyde dimethylhydrazone, thepH of the aqueous extract was found to be 7 and reduction of thehydrazone concentration to 0.005% and therebelow still gavestabilization qualities.

(B) The composition of Example IV(A) Was employed except that 0.02% byweight of diisobutylene (based upon the quantity of trichloroethylene)was admixed therewith. The pH was found to be 6. When an equivalentquantity of the formaldehyde dimethylhydrazone was employed, however, apH of 7 was obtained.

Example V The stabilization system of Example IV(B) was used except forthe omission of the hydroquinone monomethyl ether. The compositioncontaining 0.01% by weight of the acetaldehyde dimethylhydrazone had apH of only 6 whereas that containing an equivalent quantity (by weight)of formaldehyde dimethylhydrazone gave a pH of 7. Reduction of theconcentration of the hydrazone in each case to 0.005% by weight led tocomplete loss of stabilization qualities for theacetaldehyde-dimethylhydrazone composition, whereas that containing theformaldehyde dimethylhydrazone of the present invention shows effectivestabilization.

When any of the aforementioned compositions containing formaldehydedimethylhydrazone are employed, they are produced by dissolving theepoxide and phenol in themselves or in the diisobutylene which isadvantageous for this purpose. The solutions are then introduced intothe trichloroethylene with the composition being repeatedly recycledthrough a storage tank by a recirculating pump to homogeneouslydistribute the composition. The pH is then determined and, if it is lessthan 7, the composition is neutralized by bubbling gaseous ammoniatherethrough. After neutralization, the hydrazone is added at thesuction side of the circulating pump to obtain maximum homogenization.Finally the ammonia salts (e.g., ammonium chloride) produced by theneutralization are filtered from the mass. It has been found that thismethod is surprisingly effective in obtaining a highly stablecomposition, free from the lack of homogeneity characterizing earliercompositions of this type and affording maximum utilization of theformaldehyde dimethylhydrazone.

We claim:

1. A method of stabilizing trichloroethylene containing hydrogen,chloride, and phosgene, comprising the steps of admixing thymol in anamount ranging between substantially 0.001% and 0.01% by weight of thetrichloroethylene, or p-tertiaryamyl phenol in an amount ranging betweensubstantially 0.01 and 0.001% by weight of the trichloroethylene, orhydroquinone monomethyl ether present in an amount ranging betweensubstantially 0.001

and 0.1% by weight of the trichloroethylene with at least one epoxideselected from the group consisting of propylene oxide and butyleneoxide, said epoxide being present in an amount ranging betweensubstantially 0.05% and 0.3% by weight of the trichloroethylene;dispersing the resulting mixture in said trichloroethylene by repeatedlypumping the trichloroethylene with said mixture added thereto along arecycling path; adding gaseous ammonia to the resulting composition andprecipitating therefrom ammonia salts while neutralizing acidity of thecomposition; adding to said composition between substantially 0.001% and1% by weight of the trichloroethylene of formaldehyde dimethylhydrazonehaving the formula and thereafter filtering said ammonia salts from thecomposition, the composition being recycled by a circulating pump havingan inlet side and an outlet side, said hydrazone being added to saidcomposition at said inlet side of said pump.

References Cited UNITED STATES PATENTS 2,319,261 5/1943 Pitman 260-652.52,385,475 9/1945 Sconce 260-652.5 3,031,410 4/1962 Petering et al.260652.5 3,043,888 7/1962 Pray et al. 260-6525 OTHER REFERENCES Treybal,Mass Transfer Operations, pp. 365 to 367 (1955), TP 155. T7.

LEON ZITVER, Primary Examiner.

M. JACOB, Assistant Examiner.

U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,417,152 December 17, 1968 Germano Patron et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 45, the formula should appear as shown below:

Column 4, lines 8 and 32, "0.25%", each occurrence, should read 0.025%

Signed and sealed this 9th day of June 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

1. A METHOD OF STABLIZING TRICHLOROETHYLENE CONTAINING HYDROGEN,CHLORIDE, AND PHOSGENE, COMPRISING THE STEPS OF ADIMIXING THYMOL IN ANAMOUNT RANGING BETWEEN SUBSTANTIALLY 0.001% AND 0.01% BY WEIGHT OF THETRICHLOROETHYLENE, OR P-TERTIARYAMYL PHENOL IN AN AMOUNT RANGING BETWEENSUBSTANTIALLY 0.01 AND 0.001% BY WEIGHT OF THE TRICHLOROETHYLENE, ORHYDROQUINONE MONOMETHYL ETHER PREENT IN AN AMOUNT RANGING BETWEENSUBSTANTIALLY 0.001 AND 0.1% BY WEIGHT OF THE TRICHLOROETHYLENE WITH ATLEAST ONE EPOXIDE SELECTED FROM THE GROUP CONSISTING OF PROPYLENE OXIDEAND BUTYLENE OXIDE, SAID EPOXIDE BEING PRESENT IN AN AMOUNT RANGINGBETWEEN SUBSTANTIALLY 0.05% AND 0.3% BY WEIGHT OF THE TRICHLOROETHYLENE;DISPERSING THE RESULTING MIXTURE IN SAID TRICHLOROETHYLENE BY REPEATEDLYPUMPING THE TRICHLOROETHYLENE WITH SAID MIXTURE ADDED THERETO ALONG ARECYCLING PATH; ADDING GASEOUS AMMONIA TO THE RESULTING COMPOSITION ANDPRECIPITATING THEREFROM AMMONIA SALTS WHILE NEUTRALIZING ACIDITY OF THECOMPOSITION; ADDING TO SAID COMPOSITION BETWEEN SUBSTANTIALLY 0.001% AND1% BY WEIGHT OF THE TRICHLOROETHYLENE OF FORMALDEHYDE DIMETHYLHYDRAZONEHAVING THE FORMULA